Here are some exercises on the present perfect contrasted with the past
Try them and then correct them and ask if you don't understand the answer they give



http://web2.uvcs.uvic.ca/elc/studyzone/410/grammar/ppvpast1.htm


http://www.englishpage.com/verbpage/verbs5.htm


http://www.englishpage.com/verbpage/verbs6.htm


When you have finished you can do what you want from previous recommendations
including if you have headphones you can listen to the EASY NEWS on the virtualilc . See me if you don't know how to get there